Dynamic response stubbing in Cypress - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is dynamic response stubbing in Cypress?

Dynamic response stubbing is when you intercept a network request and provide a custom response that can change based on the test's needs or input data.

intermediate

How do you intercept a GET request and stub a dynamic response in Cypress?

Use cy.intercept() with a function as the response to return different data based on the request or test logic.

beginner

Why is dynamic response stubbing useful in testing?

It allows tests to simulate different server responses without changing the backend, making tests faster and more reliable.

intermediate

Example: What does this Cypress code do? cy.intercept('GET', '/api/user', (req) => { req.reply({ name: req.query.name || 'Guest' }) })

It intercepts GET requests to '/api/user' and replies with a JSON object where the name is taken from the query parameter or defaults to 'Guest'.

beginner

What is a best practice when choosing locators for dynamic response stubbing tests?

Use stable and descriptive selectors like data-* attributes to avoid flaky tests when UI changes.

What Cypress command is used to stub network responses dynamically?

A cy.stub()

B cy.intercept()

C cy.route()

D cy.visit()

cy.intercept() is the modern Cypress command to intercept and stub network requests dynamically.

In dynamic stubbing, how can you customize the response based on the request?

A By passing a function to req.reply()

B By changing the URL in cy.visit()

C By using cy.wait()

D By modifying the DOM directly

Passing a function to req.reply() lets you customize the response dynamically based on the intercepted request.

Why should you avoid using CSS classes as locators in tests with dynamic stubbing?

A Classes slow down the test execution

B Classes are too specific

C Classes are not supported by Cypress

D Classes can change often, making tests flaky

CSS classes often change during UI updates, which can cause tests to fail unexpectedly.

What is the main benefit of dynamic response stubbing in tests?

A Improve browser compatibility

B Speed up UI animations

C Simulate different server responses without backend changes

D Automatically generate test data

Dynamic stubbing lets you simulate various server responses easily, improving test flexibility and reliability.

Which of these is a valid way to reply with a dynamic response in cy.intercept()?

A req.reply(() => ({ statusCode: 200, body: { success: true } }))

B req.reply('static response')

C req.send()

D req.wait()

Passing a function to req.reply() allows dynamic response generation based on the request.

Explain how dynamic response stubbing works in Cypress and why it is useful.

Think about how you can change the server reply during a test.

Describe best practices for choosing locators when writing tests that use dynamic response stubbing.

Consider what makes a locator reliable over time.

Practice

1. What is the main purpose of dynamic response stubbing in Cypress tests?

easy

A. To change server responses during tests to simulate different scenarios

B. To speed up the browser rendering process

C. To automatically generate test data from the server

D. To record user interactions for playback

Solution

1. Step 1: Understand dynamic response stubbing

   Dynamic response stubbing allows tests to modify server replies on the fly to simulate various conditions.

2. Step 2: Identify the main goal

   This helps test how the app behaves with different data or errors without relying on real server responses.

3. Final Answer:

   To change server responses during tests to simulate different scenarios -> Option A

4. Quick Check:

   Dynamic stubbing = simulate different server replies [OK]

Hint: Dynamic stubbing means changing server replies during tests [OK]

Common Mistakes:

• Confusing stubbing with speeding up rendering
• Thinking it generates test data automatically
• Mixing it up with recording user actions

2. Which of the following is the correct way to stub a dynamic response using cy.intercept in Cypress?

easy

A. cy.intercept('GET', '/api/data', { status: 200, body: { value: 42 } })

B. cy.intercept('GET', '/api/data', (res) => { res.send({ value: 42 }) })

C. cy.intercept('GET', '/api/data', () => { return { value: 42 } })

D. cy.intercept('GET', '/api/data', (req) => { req.reply({ body: { value: 42 } }) })

Solution

1. Step 1: Recall cy.intercept syntax for dynamic stubbing

   To modify the response dynamically, use a callback with the request object and call req.reply() with the new body.

2. Step 2: Check each option

   cy.intercept('GET', '/api/data', (req) => { req.reply({ body: { value: 42 } }) }) correctly uses (req) => { req.reply({ body: ... }) }. cy.intercept('GET', '/api/data', { status: 200, body: { value: 42 } }) is static stubbing, C returns a value incorrectly, D uses res.send which is not Cypress syntax.

3. Final Answer:

   cy.intercept('GET', '/api/data', (req) => { req.reply({ body: { value: 42 } }) }) -> Option D

4. Quick Check:

   Dynamic stub uses req.reply() callback [OK]

Hint: Use req.reply() inside intercept callback for dynamic response [OK]

Common Mistakes:

• Using static object instead of callback for dynamic stubbing
• Returning response instead of calling req.reply()
• Using incorrect callback parameter names

3. Given the following Cypress code, what will be the response body when the app requests '/api/user'?

cy.intercept('GET', '/api/user', (req) => {
  const id = req.query.id
  if (id === '1') {
    req.reply({ body: { name: 'Alice' } })
  } else {
    req.reply({ body: { name: 'Guest' } })
  }
})

The app calls fetch('/api/user?id=1'). What is the response?

medium

A. Empty response body

B. { name: 'Guest' }

C. { name: 'Alice' }

D. An error occurs because req.query is undefined

Solution

1. Step 1: Analyze the intercept callback logic

   The callback checks req.query.id. If it equals '1', it replies with { name: 'Alice' }, else { name: 'Guest' }.

2. Step 2: Check the request URL query

   The app calls '/api/user?id=1', so req.query.id is '1'. Therefore, the response is { name: 'Alice' }.

3. Final Answer:

   { name: 'Alice' } -> Option C

4. Quick Check:

   Query id '1' returns Alice [OK]

Hint: Match query params in req.query to decide response [OK]

Common Mistakes:

• Assuming req.query is undefined in Cypress intercept
• Ignoring query parameters in the stub
• Confusing string and number types in comparison

4. Identify the error in this Cypress dynamic stub code:

cy.intercept('POST', '/api/login', (req) => {
  req.reply({ statusCode: 200, body: { token: 'abc123' } })
})

The test fails with an error about req.reply not being a function. What is wrong?

medium

A. The callback receives req but req.reply is not a function; should use req.continue

B. The callback parameter should be interception and interception.reply used

C. The callback parameter is correct, but req.reply is only available on res

D. The callback parameter should be named res instead of req

Solution

1. Step 1: Understand intercept callback parameter

   The callback receives an interception object, often named interception, which has the reply method.

2. Step 2: Identify the naming and usage error

   Using req as parameter is allowed but req.reply is not a function because the object is not the request but the interception. The correct approach is to name it interception and call interception.reply().

3. Final Answer:

   The callback parameter should be interception and interception.reply used -> Option B

4. Quick Check:

   Use interception.reply() in intercept callback [OK]

Hint: Use interception.reply(), not req.reply(), in intercept callback [OK]

Common Mistakes:

• Confusing request object with interception object
• Using req.reply() which does not exist
• Misnaming callback parameter causing method errors

5. You want to stub a GET request to '/api/items' so that the response body depends on a query parameter 'type'. If 'type' is 'fruit', respond with { items: ['apple', 'banana'] }. If 'type' is 'vegetable', respond with { items: ['carrot', 'lettuce'] }. Otherwise, respond with { items: [] }. Which code correctly implements this dynamic response stubbing?

hard

A. cy.intercept('GET', '/api/items', (interception) => {
const type = interception.query.type
if (type === 'fruit') {
interception.reply({ body: { items: ['apple', 'banana'] } })
} else if (type === 'vegetable') {
interception.reply({ body: { items: ['carrot', 'lettuce'] } })
} else {
interception.reply({ body: { items: [] } })
}
})

B. cy.intercept('GET', '/api/items', (req) => {
if (req.query.type === 'fruit') {
req.reply({ items: ['apple', 'banana'] })
} else if (req.query.type === 'vegetable') {
req.reply({ items: ['carrot', 'lettuce'] })
} else {
req.reply({ items: [] })
}
})

C. cy.intercept('GET', '/api/items', (req) => {
const type = req.query.type
if (type === 'fruit') {
req.reply({ body: { items: ['apple', 'banana'] } })
} else if (type === 'vegetable') {
req.reply({ body: { items: ['carrot', 'lettuce'] } })
} else {
req.reply({ body: { items: [] } })
}
})

D. cy.intercept('GET', '/api/items', (interception) => {
const type = interception.query.type
if (type === 'fruit') {
interception.send({ body: { items: ['apple', 'banana'] } })
} else if (type === 'vegetable') {
interception.send({ body: { items: ['carrot', 'lettuce'] } })
} else {
interception.send({ body: { items: [] } })
}
})

Solution

1. Step 1: Identify correct parameter and method usage

   The callback parameter should be named interception (or similar) and use interception.reply() to send the response with a body property.

2. Step 2: Check each option for correctness

   cy.intercept('GET', '/api/items', (interception) => { const type = interception.query.type if (type === 'fruit') { interception.reply({ body: { items: ['apple', 'banana'] } }) } else if (type === 'vegetable') { interception.reply({ body: { items: ['carrot', 'lettuce'] } }) } else { interception.reply({ body: { items: [] } }) } }) correctly uses interception.query.type and calls interception.reply({ body: ... }). cy.intercept('GET', '/api/items', (req) => { if (req.query.type === 'fruit') { req.reply({ items: ['apple', 'banana'] }) } else if (req.query.type === 'vegetable') { req.reply({ items: ['carrot', 'lettuce'] }) } else { req.reply({ items: [] }) } }) misses body wrapper. cy.intercept('GET', '/api/items', (req) => { const type = req.query.type if (type === 'fruit') { req.reply({ body: { items: ['apple', 'banana'] } }) } else if (type === 'vegetable') { req.reply({ body: { items: ['carrot', 'lettuce'] } }) } else { req.reply({ body: { items: [] } }) } }) uses req but req.reply is not a function. cy.intercept('GET', '/api/items', (interception) => { const type = interception.query.type if (type === 'fruit') { interception.send({ body: { items: ['apple', 'banana'] } }) } else if (type === 'vegetable') { interception.send({ body: { items: ['carrot', 'lettuce'] } }) } else { interception.send({ body: { items: [] } }) } }) uses interception.send which is not a Cypress method.

3. Final Answer:

   Option A code correctly implements dynamic response stubbing with query check and reply -> Option A

4. Quick Check:

   Use interception.reply({ body }) and check interception.query [OK]

Hint: Use interception.reply({ body }) and check interception.query.type [OK]

Common Mistakes:

• Using req.reply() which is undefined
• Omitting the body wrapper in reply
• Using interception.send() which does not exist